The invention relates to a hinge provided with a first part and a second part, which parts are able to turn relative to one another from a first position of the hinge into a second position of the hinge, the hinge being provided with a locking element for locking the hinge in the first position thereof, which locking element can move between a first position for releasing the hinge and a second position for locking the hinge.
The hinge according to the present invention is in particular suitable as an orthopedic knee joint. Orthopedic knee joints are, for example, used by patients who are not capable of stabilising the knee joint without aids. Without aids, the knees of such patients would give way when they walk. When walking, the leg moves from the point in time that the heel makes contact with the ground from a position in which it is stretched forward into the so-called mid-position stage in which the leg is essentially perpendicular under the body. Because the body is moving forward relative to the leg, the leg will then be pointing somewhat backwards with respect to the body. The leg then returns via the so-called swinging stage back to the initial position in which the heel makes contact with the ground.
For paralysis patients, for example, in order to be able to walk safely it is necessary that an orthopedic knee joint stabilises the patient's knee at the end of the standing stage, but in any event from the point in time when the heel of the foot comes into contact with the ground to at least the mid-position stage. The simplest solution for achieving this is to make use of an orthesis that fixes the thigh relative to the lower leg when walking. This can be effected, for example, by means of a hinge that is locked while walking. At the point in time when a user sits down, the user can unlock the hinge in order to make it possible to bend the leg. A significant disadvantage of a hinge of such simple construction is that the user has to walk with a stiff leg. The ease of use of orthopedic knee joints is appreciably improved if the orthopedic knee joint is automatically unlocked when the swinging stage starts. With automatic unlocking of the hinge, a user is able to walk in a normal manner. At the point in time when the leg is placed on the ground, the knee is stabilised with the aid of the orthopedic knee joint, so that the user can bear safely on the locked knee. The hinge is unlocked at the point in time when the swinging stage has to start. This can take place safely because the weight of the user has then been transferred to the other leg.
Orthopedic knee joints with which the joint can be unlocked at the start of the swinging stage are known in the state of the art. U.S. Pat. Nos. 5,490,831 and 2,943,622 and European Patent Application EP 0 872 224 disclose knee joints with which the presence of stress on a user's heel is used as a signal for locking the knee joint. According to these publications a detection element is present in the heel, which detection element is, for example, connected by a cable or rod to a locking element. As long as the detection element detects that stress is being exerted on the heel, the joint is locked by means of the locking element. However, as soon as there is no longer any stress on the heel, the knee joint is released. A significant disadvantage of the solution according to the said documents is that the knee joint will also be unlocked if stress is exerted on, for example, the front of the user's foot. If the user is negotiating an obstacle, such as, for example, a kerb, with his/her leg, the detection element will not detect any stress on the heel and will release the hinged joint. The user's knee joint will consequently give way. As a result of this limitation, the solution according to the abovementioned documents is impractical and, moreover, dangerous. An alternative solution for providing automatic unlocking of the joint is disclosed in U.S. Pat. No. 3,826,251. According to this US Patent the presence of an axial force on the hinge is used to either lock or release the hinge. A significant disadvantage of this solution is that the bulk of the reactive force from the ground is absorbed by the leg. That is to say this reactive force is not absorbed by the hinge and can also be not be detected by the hinge. This means that these hinges do not work well in practice.
U.S. Pat. No. 4,632,096 discloses a hinge that can be released by turning the foot relative to the leg. A cable is attached to the foot, which cable is connected to a locking element in the knee joint. By turning the foot, locking of the hinge can be released with the aid of the cable.
The disadvantage of the solution according to this US Patent is that unlocking can take place only by active turning of the foot. This means that the user must be prepared to turn his/her foot at every step. Furthermore, in this solution a coupling is always needed between the knee joint and the foot or the ankle joint. This makes the system susceptible to malfunctions and in the majority of cases the aid in which the knee joint is incorporated will have to be equipped with a foot section. Moreover, here again the functioning of the system is dependent on the ground surface.